Thermoplastic polyesters represented by polyethylene terephthalate or polybutylene terephthalate are superior in mechanical characteristics, chemical resistance and electric characteristics, and thus are used in a wide variety of fields including automotive parts and electric/electronics parts. With the diversification of the markets in these fields, thermoplastic polyesters are required to have higher or special performance and a higher quality, depending on their applications. Polytrimethylene terephthalate resin, among other polyester resins, is superior in mechanical characteristics, weatherability, heat aging resistance and hydrolysis resistance. It also has superior properties such that when reinforced with inorganic fillers, the appearance of the molding is not impaired and warpage of the molding hardly occurs. Its uses can thus be extended to a wide variety of fields.
For the application with electric/electronics parts, which is one of the fields where the application of polytrimethylene terephthalate resin is expected to extend, a level of flame retardance based on the UL-94 standard by UNDERWRITERS LABORATORIES is required.
To satisfy this requirement, compositions containing halogen type flame retardants have conventionally been studied. For example, JP-A-50-49361 proposes a resin composition consisting of polypropylene terephthalate or polybutylene terephthalate, decabromodiphenyl ether, antimony trioxide and asbestos. U.S. Pat. No. 4,131,594 proposes a resin composition consisting of polytrimethylene terephthalate and a graft copolymer, a halogen type flame retardant, such as a polycarbonate oligomer of decabromobiphenyl ether or tetrabromobisphenol A, antimony oxide and glass fiber. However, such a halogen type flame retardant generates corrosive hydrogen halide upon combustion and also is suspected of discharging toxic substances such as dioxin. There is thus a movement to control the use of plastic products containing a halogen type flame retardant.
In this movement, JP-A-2000-169681, for example, proposes a flame retardant resin composition consisting of polytrimethylene terephthalate and red phosphorus. However, the use of this composition is limited because it has a red color and possibly generates phosphine gas during processing. Further, EP 0955338, EP 0955333 and JP 310284 propose resin compositions consisting of polybutylene terephthalate, melamine cyanurate, ammonium polyphosphate or melamine polyphosphate, phosphate ester and glass fiber. These compositions, however, have large warpage deformation and a poor appearance when molded, and thus cannot sufficiently satisfy the market's needs.